Wednesday forecast: Humid start, potential for heavy rainfall later as heat breaks in Chicagoland

The recent run of high heat and humidity around Chicagoland is about to break.

And with that will come potentially heavy rainfall.

The air is still thick and humid to start Wednesday, with early-morning temperatures already near 80 in some locations and dew points again into the 70s. But the warmest temps of the day will come early.

A first chance for showers and storms arrives around midday, mainly for far northwest locations. After an afternoon break, waves of showers and storms are likely around Chicagoland in the evening hours and into Wednesday night, bringing gusty winds and the potential for heavy rainfall (see more below).

With that, the heat will break, with highs for the rest of the week and into the coming weekend staying in the 70s and low 80s (see more below).

Wednesday: Severe risk 

While we could get heavy rainfall totals, the risk for severe weather remains low.

The Chicago area is in a Level 1 of 5, or Marginal Risk, for seeing a strong or severe thunderstorm. The primary hazard would be isolated damaging winds.   

Wednesday: Excessive rainfall

The atmosphere will continue to be rather humid, meaning any storm that develops will have plenty of moisture to work with. The Chicago area is in a heightened risk (Level 2 of 4) for excessive rainfall capable of producing localized flooding.

With that heavy rainfall potential, a Flood Watch will be in effect for most of Chicagoland from 1 p.m. Wednesday to 1 p.m. Thursday.

Wednesday: Rainfall timeline

A first wave of showers and storms will move into the area around midday, but that wave isn’t expected to bring the heaviest, most widespread rainfall totals.

That will come later Wednesday, starting in the late afternoon to early evening.

Wednesday: Forecast total rainfall

As is the case for any summertime thunderstorm, rains do not fall homogenously, meaning some areas will see far more rainfall than others,

But the potential exists for some locations to see up to 2 or more inches.

Wednesday: Temperature outlook

The 90s are gone for at least the next week to 10 days.

Wednesday highs are likely to reach only the upper 70s to lower 80s, a level more than 10 degrees cooler than Tuesday afternoon. And the warmest temps Wednesday will come early, with temps dropping as the wind picks up and rainfall moves in later.

Wednesday: Beach forecast

The recent hot and humid conditions have also brought some great days to jump into Lake Michigan and cool off at Chicagoland beaches.

Not so for the rest of this week.

Steady north/northeast winds off the lake will kick up quite a chop on the lake in the coming days, through Friday. Waves of 5 to 8 feet will create hazardous boating conditions and life-threatening currents for swimmers.

A Beach Hazards Statement is in effect for lakeside counties from Wednesday afternoon through Friday afternoon. So while cooler air may create some pleasant conditions to sit on the beach, plan to stay out of the water through at least Friday.

Wednesday: Sunburn forecast

A significant pattern change to much cooler weather is taking shape, especially by Thursday and into the coming weekend.    

Chicago forecast highs and departures from normal

An extended string of sub-normal highs are on tap, quite a change from the recent heat.  

Forecast average max temperature departure from normal: Aug. 1-5

The start of August brings quite a change from the persistent warmth that dominated much of July. Instead, much of the Central and Eastern U.S. are set to enjoy cooler, more comfortable conditions. 

Forecast 850-millibar (1 mile above the ground) temperature anomaly

This is a good proxy indicator of how temperatures will respond at the surface. The orange and red colors represent areas of above normal temperatures, while the blue shading represents areas of below normal temperatures. 

This animation shows the transition to much cooler weather in coming days:

Saturday AM lows

A taste of fall in the air, as low temps will drop into the 50s by Saturday morning for areas away from the lake. Give the AC a break!